how to calculate MTBF of a PLC system

[omsumitam]

Can anybody tell me How to Calculate the

MTBF- Maen Time Between failure
PDF - Probability of undetected failure per hour
PFD - Product Probability of failure on demand

of a PLC system. formula or Link

If i am using a URL base communication b/w two distant scada based Engineering System and using a Redundant Internet connection of say Airtel and Vodafone. then is it possible to calculate the MTBF of Communication offered .

Thanks in advance.

 

[RussB]

I am sure that someone can, but....
If the algorithm does not account for errors in implementation AND abusive users, it will not be very accurate.
Nearly all failures I've seen in more than 30 years have been "user" triggered in some way.

 

[ndzied1]

I am sure that someone can, but....
If the algorithm does not account for errors in implementation AND abusive users, it will not be very accurate.
Nearly all failures I've seen in more than 30 years have been "user" triggered in some way.

I have seen two lightning triggered failures...

 

[Mickey]

Do you have documented failures over a given period of time? I think you need this first.

Or call the vendors, they usually have numbers like that.

http://en.wikipedia.org/wiki/Mean_time_between_failures

http://www.google.com/search?q=Prob...s=org.mozilla:en-US:official&client=firefox-a


http://www.google.com/search?q=+Pro...s=org.mozilla:en-US:official&client=firefox-a

 

[omsumitam]

Thanks to all ,for your responses
If considering "Lightning" could be a failure cause and still i go with GSM/GPRS Modem for communication b/w two control stations who are 70KM .Can you help me out of the these :

LIMITATION of Following:

1. GSM modem between two Control Stations without repeater if specification are
2W @ 800-900MHz
and 1W @ 800-1900MHz,
Freq.-800,900---,1900 EGSM

2. Shielded Twisted Pair of say 6 Pair x 1.5 sq.mm underground 900mm-1 meter in terms of EMC (Electro Magnetic Compatibility)or ETL .